DE69023573T2 - Aqueous hydroxyethyl cellulose suspension. - Google Patents

Abstract

An aqueous suspension comprising 8 to 28%, by weight of the total suspension, of water-soluble hydroxyethylcellulose dispersed in an aqueous solution comprising 20 to 35%, by weight of the total potassium carbonate and water, of potassium carbonate, 0.2 to 0.8%, by weight of the total suspension, of a wetting agent having a HLB of 6 to 9, and 0.08 to 0.6%, by weight of the total suspension, of a water-soluble or water-swellable thickener; a process for preparing the same; and use of the same in a variety of applications, are disclosed.

Description

The invention relates to stable aqueous suspensions of water-soluble hydroxyethylcellulose, a process for producing the same and the use of the same in a variety of applications. Background of the invention

Water-soluble hydroxyethyl cellulose (HEC) is a nonionic polymer useful in many industrial processes and consumer products. Traditionally, it has been used in its dry particulate form. Problems associated with dry HEC include undesirable dust generation, poor dispersibility when added to aqueous systems, and undesirably long dissolution times.

The dust associated with dry, particulate HEC presents the same traditional handling problems encountered with similar particulate materials. A major concern is the potential for dust explosions.

HEC is hygroscopic and absorbs water from the air, which can cause particle agglomeration. Such agglomerated particles are very difficult, if not impossible, to disperse in an aqueous system.

When added to aqueous systems, HEC tends to agglomerate or form lumps. Agglomeration can be reduced in many cases by adding the HEC to the aqueous system slowly while stirring. Slow dissolution significantly reduces the speed of manufacturing processes.

For the reasons stated above, plant operators want a fast, effective and easy way to introduce HEC into an aqueous system. That is, HEC users want a stable, concentrated HEC suspension that can be used to easily introduce HEC into aqueous solutions without the formation of agglomerates or lumps, and that can be handled without the problems associated with dry HEC powder.

Girg et al., in U.S. Patent No. 4,283,229 and in EP-A-3582, disclose that a stable suspension can be prepared by adding a non-ionic, water-soluble cellulose ether derivative to a 4 to 12% solution of an electrolyte when alumina is added to the suspension. Suitable electrolytes are described as including metal or ammonium salts of mineral or organic acids, particularly salts containing an alkali metal ion, an alkaline earth metal ion, an earth metal ion, or a zinc, copper, iron or manganese ion as the cation and a sulfate, carbonate, silicate, sulfite, halogen, phosphate, nitrate, nitrite, acetate, formate, tartrate or citrate ion, including their hydrogen salts, as the anion. Examples V1 and V2 show the dispersion of 25 wt.% methylhydroxyethylcellulose using 28 and 20 wt.% potassium carbonate, respectively.

EP-A-39128 discloses the suspension of a water-soluble polymer in an organic, liquid, non-solvent suspension medium comprising an alcohol-soluble thickener such as hydroxypropyl cellulose and a surfactant having an HLG (hydrophilic-lipophilic balance) between about 10 and 20.

EP-A-2368 discloses the use of a concentrate of a particulate polymer (e.g. ethylene oxide) in a water-insoluble organic vehicle such as a petroleum-based liquid hydrocarbon and a surfactant having an HLG in the range of 3 to 5 or 9 to 13 for dissolving the polymer in water.

FR-A-2600267 describes porous granules of biopolymers of the xanthan gum type.

The inventor has studied the dispersion of HEC and found that large amounts of this polymer can be dispersed in an aqueous system using the combination of potassium carbonate, wetting agent, thickener and dispersant amounts of this invention according to claim 1. Summary of the Invention

Accordingly, the invention is an aqueous suspension comprising 8 to 28% by weight of the total suspension of water-soluble hydroxyethylcellulose (HEC) dispersed in an aqueous solution comprising 20 to 35% by weight of the total amount of potassium carbonate and water of potassium carbonate, 0.2 to 0.8% by weight of the total suspension of a wetting agent having an HLG of 6 to 9 and 0.08 to 0.6% by weight of the total suspension of a water-soluble or water-swelling thickener. The suspension further comprises 0.05 to 0.5% by weight of a dispersant having an HLG higher than 14. The invention also relates to a process for preparing such a suspension and a process for preparing an aqueous solution of dissolved HEC using such a suspension. Detailed Description of the Invention

The invention is a stable, pourable, liquid suspension containing high concentrations of water-soluble hydroxyethylcellulose (HEC).

"Suspension", "dispersion", "solution" and other terms are often confused. Therefore, it should be clarified It should be noted that "suspension" and "dispersion" may be used interchangeably herein to refer to a system in which solid particles (HEC) are dispersed in a liquid (water). It should also be clarified that "solution" means a homogeneous mixture of a solvent (e.g. water) with a solute (e.g. dissolved potassium carbonate, dissolved HEC, etc.).

The HEC dispersed in accordance with the invention is nonionic and water soluble, e.g. such that the solution viscosity is on the order of 1,000 mPa s (1,000 centipoise) or more in a 5 wt.% aqueous HEC solution and at larger amounts, e.g. 10 wt.%, the viscosities of their aqueous solutions are extremely high or they form a gel. Because of this very high viscosity, these polymers cannot normally be pumped or handled (dissolved) in aqueous media when their concentration exceeds 5 to 10 wt.%. Typically, the polymers of this invention have a molar hydroxyethyl substitution (number of hydroxyethyl groups per anhydroglucose unit) of about 1.0 to about 4.2, preferably about 1.8 to over 3.0. Suspensions according to the invention contain at least 8% by weight, preferably 18 to 28% by weight and very preferably 22 to 26% by weight of the total suspension of particulate HEC.

The HEC may be treated with aldehydes such as glyoxal, but such treatment is not essential for the purposes of the invention.

The aqueous solution comprises 20 to 35%, preferably 25 to 33%, and most preferably 29 to 32% by weight of the total amount of potassium carbonate and water potassium carbonate. The desired concentration of potassium carbonate in water varies with the type and amount of hydroxyethyl cellulose.

Wetting agents are molecules that have both a hydrophilic and a lipophilic character. The wetting agents useful in this invention have a hydrophillipophilic Equilibrium (HLG) value in the range of 6 to 9. Wetting agents are sorbitan fatty acid esters (including polyoxyethylene sorbitan fatty acid esters) and polyoxyethylene nonylphenol esters. Illustrative are sorbitan monolaurate and mixtures thereof with polyoxyethylene sorbitan monolaurate (ratio of 20:80 to 0:100) or sorbitan monostearate (ratio of 40:60 to 0:100), sorbitan monopalmitate, lecithin and polyoxyethylene nonylphenol ether, with sorbitan monolaurate being most preferred. The wetting agent is used in an amount of 0.2 to 0.8% based on the total weight of the suspension.

A water-soluble or water-swelling thickener (also known as a "suspending agent") is also useful for suspending hydroxyethyl cellulose in accordance with the invention. Illustrative are bentonite, carboxyvinyl polymers (e.g., Carbopol polymers, B.F. Goodrich, Cleveland, Ohio), and xanthan gum. Xanthan gum is preferred. Thickeners are generally used in an amount of 0.08 to 0.6%, preferably 0.14 to 0.25%, and most preferably 0.16 to 0.22%, based on the total weight of the suspension.

This suspension of the invention also contains dispersants, i.e. molecules with higher HLG values (generally HLG higher than 14). Dispersants are polyoxyethylene sorbitan fatty acid esters and alkali salts of polyacrylic acids, e.g. polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monolaurate and the sodium and ammonium salts of polyacrylic acid. Preferred are alkali salts of acrylic acid. Most preferred is the sodium salt of polyacrylic acid. Dispersants are used in an amount of 0.05 to 0.5 wt% of the total suspension. Higher amounts of polyoxyethylene sorbitan fatty acid esters, e.g. 0.08% or more, are generally necessary for good appearance. Preferably the dispersant is present in an amount of 0.1% or more.

Other additives that may be used include colorants, dispersants, surfactants, glycols and thickeners. These are generally used in amounts up to 10%, preferably 0.5 to 2%, based on the weight of the total suspension.

The suspensions of this invention can be prepared by dissolving potassium carbonate in water to form an aqueous salt solution and then dispersing the HEC in this solution with stirring. The wetting agent can be added at any time, but is preferably added before adding the HEC to the salt solution. The thickener can be added at any time, but is preferably added after the potassium carbonate and before the HEC and wetting agent(s). The dispersing agent can be added at any time, but is preferably added after the HEC (as are the salt, thickener and wetting agent). In the case where other additives are used, they are typically added to the water before the salt.

By "stable" is meant that the dispersed phase (water-soluble hydroxyethyl cellulose) and the aqueous phase do not separate for a minimum period of time after preparation or, if separation does occur, the hydroxyethyl cellulose can be easily redispersed with little agitation. Stability is a function of the type of hydroxyethyl cellulose used as well as the concentration of hydroxyethyl cellulose, salt, etc. Suspensions of the invention have been shown to be stable over long periods of time, e.g., nine months. The stability of the suspensions of this invention can be further improved by mixing the dispersion under vacuum to remove entrained air. The extended stability of the suspensions of this invention allows them to be prepared in one location and transported to another location where they are to be used.

The viscosity of the suspensions of this invention is relatively independent of the molecular weight (or solution viscosity) of the hydroxyethylcellulose in suspension. Instead, the viscosity is proportional to the amount of hydroxyethylcellulose present. Furthermore, the suspension viscosity is inversely proportional to the potassium carbonate concentration. Accordingly, to suspend larger amounts of HEC, it is necessary to use larger potassium carbonate concentrations.

The HEC suspensions of this invention are useful in virtually all applications in which dry, water-soluble hydroxyethyl celluloses are currently used, the only limitation being that the potassium carbonates may not be desirable in some applications. The applications in which the dispersions of this invention can be used include, for example, water clarification, mineral processing, food and pharmaceutical thickening, cosmetic thickening, agricultural thickening, oil field applications, building products (e.g., sealing cements), ceramics, latex paints, paper coatings, emulsion polymerization, suspension polymerization, carpet reinforcement, etc. Advantages of using the highly concentrated HEC suspensions of this invention include the ability to control the thickening effect of the HEC (thickening time is significantly reduced), ease of handling and dosing control (automated addition of HEC is possible for many applications), avoidance of dusting of the polymer, avoidance of clumping, etc.

The suspensions can be added to aqueous systems (e.g. aqueous solutions) by simply adding, e.g. pouring, the suspension into the aqueous system. Stirring improves dissolution. The suspension can also be sprayed, squirted, etc. where desired for a specific end use.

The invention is demonstrated in the following examples, which are intended to be illustrative and not limiting, in which all parts, percentages, etc. are by weight. Example 1

In each case, an aqueous potassium carbonate solution was prepared by dissolving potassium carbonate in water. In the case where a wetting agent was used, it was added before the HEC. If a thickener was used, it was added after the potassium carbonate and before the HEC and the wetting agent. In the case where polyacrylic acid was added as a dispersant, it was added after the HEC. In the case where polyoxyethylene sorbitan monostearate was added as a dispersant, it was added with or after the HEC. TABLE 1 TABLE 1 (continued)

The Most suspensions are storage stable. Exceptions are sample E, which is caused by too low a salt content resulting in dissolution of the HEC, and sample T, which is caused by the absence of a thickener.

Stable suspensions can be obtained without the presence of a wetting agent and a dispersing agent. However, such suspensions often have an inferior appearance (i.e. they have the appearance of a non-homogeneous apple sauce, causing pumping/dosing problems).

Samples (O) and (Z) show that a wetting agent is required for good appearance.

The presence of a dispersant is not always necessary for good appearance (see e.g. samples (A) and (K)), but poor appearance can result if the dispersant(s) are not used in sufficient amounts (see e.g. sample (W)). Example 2

Solutions were prepared by adding 5 g of the suspensions prepared according to the procedure of Example 1 into 100 g of dilution water. The suspensions and polymers used and the results are listed in Table 2. TABLE 2 SOLUTIONS PREPARED FROM HEC SUSPENSIONS

It was observed that the suspensions of this invention dispersed and then rapidly thickened the water to form viscous solutions.

1. An aqueous suspension of a nonionic water-soluble hydroxyethylcellulose and salt, characterized in that the aqueous suspension comprises at least 8 to 28% by weight of the total aqueous suspension of water-soluble hydroxyethylcellulose dispersed in an aqueous solution comprising 20 to 35% by weight of potassium carbonate based on the total weight of potassium carbonate and water, 0.2 to 0.8% by weight of a wetting agent having a HLG (hydrophilic-lipophilic balance) value of 6 to 9, selected from the group consisting of sorbitan fatty acid esters, polyoxyethylene nonylphenol esters, sorbitan monolaurate, lecithin, polyoxyethylene nonylphenol ether, sorbitan monostearate, sorbitan monopalmitate and mixtures of sorbitan monolaurate with polyoxyethylene sorbitan monolaurate, and 0.08 to 0.6% by weight of a water-soluble or water-swelling thickener, both based on the weight of the total suspension, and further comprising 0.05 to 0.5% by weight of a dispersant having an HLG value greater than 14, which is either an alkali salt of polyacrylic acid or a polyoxyethylene sorbitan fatty acid ester.

2. Aqueous suspension according to claim 1, further characterized in that the thickener is selected from the group consisting of bentonite, carboxyvinyl polymers and xanthan gum.

3. Process for the preparation of an aqueous suspension of a nonionic water-soluble hydroxyethylcellulose and salt, characterized in that the process comprises the steps:

(A) Preparation of an aqueous potassium carbonate solution;

(B) adding a water-soluble or water-swelling thickener and a wetting agent to the aqueous potassium carbonate solution;

(C) dispersing a hydroxyethyl cellulose in the aqueous solution to prepare an aqueous suspension; and

(D) Addition of a dispersant at any time includes.

4. The method according to claim 3, further characterized in that the dispersant such as an alkali salt of polyacrylic acid or a polyoxyethylene sorbitan fatty acid ester is added in an amount of 0.05 to 0.5% by weight based on the total weight of the aqueous suspension.